1. Field of the Invention
The present invention relates to a digital broadcast receiving apparatus for receiving digital broadcasts. In digital broadcast services, various broadcast programs (contents), such as image broadcast programs, image broadcast program service information, data broadcast programs, downloadable data, and music broadcast programs, are individually digitized, multiplexed, and thereby broadcasted. Types of digital broadcasts to be handled by the present invention include CS digital broadcasts, BS digital broadcasts, ground-wave digital broadcasts, and CATV digital broadcasts.
2. Description of the Related Art
In digital broadcast services, plural broadcast programs are multiplexed and broadcasted in one channel. Plural channels are used in the services.
Transmitted modulated waves are received by tuners; demodulation and error correction thereof are performed in demodulator sections to generate transport streams (each of which will be referred to as a “TS”, hereinbelow); and a TS-separating section retrieves streams each consisting of TS packets (each of which may simply be referred to as a “packet”, hereinbelow). For example, an acquired image stream is converted by an image decoder into image information, and an image is displayed on the screen of a monitor. An acquired audio stream is converted by an audio decoder into an audio signal stream, and the signal steam is output from a speaker as audio. Acquired transport information is transferred to a digital recording device via a digital interface and is recorded therein.
With a digital broadcast receiving apparatus capable of processing only TSs of a single system, there occur cases where a plurality of contents cannot be simultaneously obtained.
For example, when a TS including a viewing-desired broadcast program and a TS including an image-recording-desired broadcast program exist on different transmission lines, screen-viewing and image-recording cannot be simultaneously performed.
In addition, as in the case of CS digital broadcasting, in the case where a broadcast-program layout information (service information (SI)) for making a broadcast program table can be transmitted only from a designated TS, when a viewing broadcast program is included in a TS differing from that including the SI, the broadcast program table cannot be displayed during screen-viewing.
Also, in the case where downloadable data can be transmitted only from a specific TS, when a viewing broadcast program is included in a TS that is different from that including the downloaded program, a new program cannot be downloaded during screen-viewing.
Similarly, in the case where a TS including a broadcast program desired to view is different from a TS including a data broadcast such as an EMD (electronic music delivery), the data broadcast cannot be received during screen-viewing.
A plurality of TSs can selectively be received if the receiver is configured such that a plurality of tuners and a plurality of demodulator sections are provided, and the plurality of demodulator sections is connected to and/or disconnected from a single TS-separating section. However, as long as the single TS-separating section is provided, no change is made in that processing can be performed only in units of one TS.
If the receiver is configured such that either the TS-separating sections are provided corresponding in number to TSs desired to process, arbitrary contents included in a plurality of different TSs are combined so as to be obtained at the same time. In this case, however, the cost would be significantly increased, and the size of the receiver would be anyway increased.
As a technique that allows plural TSs to be processed, and in addition, that allows arbitrary contents to be extracted from arbitrary TSs, a digital broadcast receiving apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 11-122556 (or, 1999-122556).
The digital broadcast receiving apparatus disclosed in the above-referenced publication comprises plural tuners, plural demodulator sections individually connected to tuners, and a multiplexer section provided between the plural demodulator sections and a TS-separating section.
The multiplexer section performs time-division multiplexing of TSs of plural systems in units of a packet to thereby generate a new TS. It is characterized in that the time-division multiplexing is performed at a frequency higher than the sum of transmission bit rates in plural-system broadcast methods. The multiplexing is performed in this manner in order to multiplex the plural TSs as in the state of including all packets, each of which is included in the individual TS.
However, the digital broadcast receiving apparatus disclosed in Japanese Unexamined Patent Application Publication No. 11-122556 (or, 1999-122556) arises the following problems.
In order to perform the time-division multiplexing at a frequency higher than the sum of transmission bit rates of individual broadcast signals, a high-performance oscillator for generating such a high frequency is required. Even with such an oscillator, time-division multiplexing at a frequency higher than that generated by the oscillator cannot be performed. Therefore, an expensive oscillator must be used.
In addition, in the case where the bit rate of the single new TS generated by the multiplexing is higher than a predetermined value, it is difficult for such a rear-stage TS-separating section to process TSs. Therefore, when plural TSs are multiplexed in the above condition, there can occur a case where intended packets cannot be separated.
Moreover, when the same PID (packet identifier) is used for individual broadcast signal, since the same PIDs are mixed in one TS, decoding cannot be performed.
As shown as examples in the above-referenced patent application publication, when broadcast-method identifiers are allocated to all the packets, the receiver may not be able to provide the intended functions. To enable the functions, a separate TS-separating section capable of processing TSs including the broadcast-method identifiers. However, it would significantly increase the cost.